1. Field of the Invention
The present invention relates to interface switching devices for adapting an apparatus provided with a PS/2interface for a USB interface, and in particular, to an interface switching device using a converting adapter to perform automatic switching.
2. Description of the Related Art
Keyboards and mice have been used as devices for inputting data to computers. In these keyboards and mice, an interface called xe2x80x9cPS/2xe2x80x9d is mainly used. However, recently, instead of the PS/2 interface, an interface called the xe2x80x9cUSB (Universal Serial Bus)xe2x80x9d is in the process of coming into use as an interface not only for keyboards and mice but also for peripheral devices.
The PS/2 interface completely differs from the USB interface in connector shape and data format. Accordingly, for using the PS/2 interface, a PS/2 device must be connected to a PS/2 port provided in a computer, and for using the USB interface, a USB device must be connected to a USB port provided in a computer.
This construction has a problem in that, since a PS/2 port will not be provided in future computers (as hosts), a conventional keyboard (as a terminal) adapted for the PS/2 interface cannot be used and a new keyboard adapted for the USB interface must be bought.
Even in the case where a computer is provided with both PS/2 and USB type ports, if devices having USB output units, such as a keyboard and a mouse, which are as many as the number of (normally two) USB ports, are connected to the USB ports, more devices cannot be connected to the USB ports. Accordingly, add-on devices for increasing the number of USB ports have been made practicable, and are on sale. Inconveniently, a user must buy such a device.
In addition, an adapter for switching the PS/2 interface and the USB interface has already been made available. The mechanism of this adapter is complex since its adapter component performs data conversion. The stability of its operation cannot be secured because the PS/2 interface and the USB interface differ from each other in signal processing in that the PS/2 interface performs signal processing on transistor-transistor logic (a process using a 0-volt signal and a 5-volt signal) and the USB interface performs differential output signal processing. The complex mechanism makes it impossible to provide an adapter with a low price.
The present invention is made for solving the foregoing problems. Accordingly, it is an object of the present invention to provide an interface switching device which switches interface types, as required, and which secures the stability of its operation without being provided with any complex mechanism.
To this end, according to the present invention, the foregoing object is achieved through provision of an interface switching device including an output unit adapted for a first interface, which is provided on the side of a terminal, an input unit adapted for a second interface, which is provided on the side of a host, and an adapter for connecting the output unit on the terminal side and the input unit on the host side. When the output unit on the terminal side is connected to the adapter, the adapter supplies identification information to the output unit on the terminal side, and an output signal from the output unit on the terminal side is switched to a signal adapted for the second interface.
When the first interface is used to establish connection between the host and the terminal, the output unit on the terminal side may be connected to the input on the host side without using the adapter. When the second interface is used to establish connection between the host and the terminal, the adapter may be connected both to the output unit (toward the terminal) adapted for the first interface and to the input unit (toward the host) adapted for the second interface. This makes it possible to perform switching between the first interface and the second interface.
In this case, the terminal needs to be provided with a generating unit which can generate both a signal adapted for the first interface and a signal adapted for the second interface.
Preferably, the identification information is supplied to the output unit on the terminal side from a line among the output lines of the first interface which is not used in the second interface.
By way of example, at the output unit on the terminal side, by providing beforehand, as an identification line, a line to be connected to the unused line in the second interface, the unused line cannot be used at all when the adapter is not connected, and the identification signal can be supplied to the output unit via the identification line when the adapter is connected. Thereby, when receiving the identification signal, the terminal can switch an output signal adapted for the first interface to an output signal adapted for the second interface, and supplies the signal to the host.
As described above, the interface switching device can be formed by a simplified mechanism in which the identification information is simply supplied to the terminal via the identification line provided beforehand at the terminal. At the terminal, the signal adapted for the second interface is generated and directly output, which makes it possible to secure sufficient stability of operation.
Preferably, the unused line is connected to a power-supply line or a ground line.
When the unused line is connected to the power-supply line, the terminal is notified of identification information fixed at a predetermined voltage via an identification line. When the unused line is connected to the ground line, the terminal is notified of identification information including a voltage fixed at zero volts (ground potential) via the identification line. The terminal detects the identification information including either voltage, thereby detecting switching from the first interface to the second interface, and an-output signal adapted for the second interface is sent to the host in accordance with the switching.
Preferably, the first interface is a PS/2 interface, and the second interface is a USB interface.
The PS/2 interface consists of, for example, six output lines. Among the six lines, two lines are not used, and either of the two unused lines may be used as an identification line. When the adapter is connected, the identification line is connected to an unused line of the adapter, and the unused line and the power-supply line or the ground line are short-circuited, whereby identification information composed of a constant voltage is supplied to the terminal via the identification line.
According to the present invention, interfaces having different types of specifications, such as a PS/2 interface and a USB interface, can be switched in accordance with circumstances. In addition, an interface switching device can be provided with a low price since it has a simplified adapter mechanism, and sufficient stability of its operation can be secured since signal conversion is not directly performed by the adapter mechanism.